The present invention relates to drive sprocket assemblies for driving saw chains of chain saws.
In Swedish Patent Application 9302842-1 there is shown a drive sprocket device for the automatic tensioning of a saw chain on chain saws, where the saw chain runs around a loose outer drive ring rolling against an inner drive sprocket of a traditional rim sprocket. The rim sprocket is characterized by having a periphery with an annular row of recesses in which the drive links of the saw chain can enter, the width of the recesses being barely larger than the thickness of the drive links, and the row of recesses bordering cylindrical surfaces of the rim sprocket on both sides. The axial alignment between the drive ring and the drive sprocket is maintained by either two radially inward flanges on the drive ring, or two radially outward flanges on the drive sprocket. This prevents such displacements that could make the drive links climb out of the recesses.
A device with two flanges extending in the same direction works well for any orientation of the drive sprocket shaft, i.e., the shaft can point up or down without the drive ring sliding therefrom.
In many applications, there is no need to be concerned about upwardly directed shafts, either because the cutting heads of the vehicle-borne chain saws cannot be turned upside down, or because hand-held chain saws are rarely operated with the drive shaft directed upwardly and are never laid down with the shaft being upwardly directed, except for service.